The pneumocardiogram (PNCG) is a record of the cardiac-induced movement of air in the trachea. The purpose of this investigation is to quantitate the relationship between the PNCG and stroke volume, and to develop an instrumentation system that will provide a non-invasive estimation of cardiac output. Specifically, we propose to quantitatively correlate the pulsatile volume of air moved in the trachea with each heart beat with the volume of blood pumped through the pulmonary artery. Once the relationship between the PNCG and stroke volume has been established, a non-invasive instrumentation system will be developed and tested in animals to obtain real-time measures of stroke volume and cardiac output. The instrument will be adapted for human use so that non-invasive assessment of cardiac performance can be monitored during surgical procedures, during the post-surgical recovery period, or during a course of therapy.